This invention relates to a cutting device which comprises a rotary blade and a non-rotatable blade which is slightly retractable from the rotary blade out of contact therewith, and which device is adapted to cut a paper web such as the paper used in the form of a roll for copying machines.
Conventional cutting devices of this type are basically constructed as shown in FIGS. 1 to 3, and comprise a rotary blade 2 and a stationary blade 1 overlapping the blade 2 with a lap progressively increasing from one end A of the lapping portion to the other end B. The rotary blade 2 is inclined at a shear angle .alpha. with respect to its shaft portions 2a. With the rotation of the rotary blade 2, both blades come into point contact with each other progressively from the one end A toward the other end B to cut a paper web (not shown) moving in the direction of the arrow of FIG. 1. The stationary blade 1 is pivotably supported on a rod 1a. A pin 1b extends from the free end of the stationary blade 1, and a spring 3 is mounted in place at one end and is connected at its other end to pin 1b for holding opposite ends of the stationary blade 1 in bearing contact with flanges 2b at opposite ends of the rotary blade 2. When both the blades come into contact with each other progressively from point-to-point with the rotation of the rotary blade 2, the stationary blade 1 is pivotally movable slightly away from the rotary blade 2.
With the device described above, the lap at the end B, if excessively large, will result in rapid wear on the blades, require an increased drive force for the rotary blade and cause much noise or other objections, whereas if it is too small, the paper will not be cut properly. Thus the lap is extremely difficult to adjust. According to the conventional structure, moreover, the side of the stationary blade 1 which is difficult to machine to a planar finish is adapted for bearing contact with the flanges 2b of the rotary blade 2 to position the blade 1 in place. The stationary blade cannot therefore be favorably machine. There is another drawback in the structure in which the stationary blade 1 is supported pivotably by the rod 1a and held in contact with the rotary blade 2 by the spring 3. Since the stationary blade 1 is of the pivotal type, it is not smoothly retractable when the rotary blade 2 rotates for cutting. This is disadvantageous in view of the attendant wear of the blades, the increased torque needed and the resulting noise.